Graphene based All-Optical Spatial Terahertz Modulator

TLDR

The authors demonstrate an all‑optical terahertz modulator based on single‑layer graphene on germanium, driven by a 1.55 µm CW laser, and propose a model attributing its performance to third‑order nonlinear optical conductivity. Static and dynamic THz transmission modulation experiments were performed on the graphene‑on‑germanium device, and the model links the modulation to the third‑order nonlinear response of the graphene monolayer. The device achieves broadband THz modulation from 0.25 to 1 THz with a 94 % depth and a 200 kHz modulation speed, confirming the predicted nonlinear effect.

Abstract

We demonstrate an all-optical terahertz modulator based on single-layer graphene on germanium (GOG), which can be driven by a 1.55 μm CW laser with a low-level photodoping power. Both the static and dynamic THz transmission modulation experiments were carried out. A spectrally wide-band modulation of the THz transmission is obtained in a frequency range from 0.25 to 1 THz, and a modulation depth of 94% can be achieved if proper pump power is applied. The modulation speed of the modulator was measured to be ~ 200 KHz using a 340 GHz carrier. A theoretical model is proposed for the modulator and the calculation results indicate that the enhanced THz modulation is mainly due to the third order nonlinear effect in the optical conductivity of the graphene monolayer.